GstO1 (CG6662, Q9VSL6) - manual literature research

No deep-research API provider was available for this review; this file records a manual
literature survey (PubMed searches plus cached full texts in publications/).

PubMed query used: (CG6662 OR GstO1 OR "glutathione S-transferase omega") AND Drosophila
(13 hits, October 2026).

Identity and nomenclature (important)

• Q9VSL6 is the product of FlyBase FBgn0035907, gene symbol GstO1, annotation ID CG6662,
  GeneID 38975, on chromosome 3L in the Omega-class GST cluster (66D) together with
  se (sepia, CG6781), GstO2 (CG6673) and GstO3 (CG6776).
• Nomenclature trap. Kim et al. 2012 (PMID:22219196) called CG6673 "DmGSTO1"
  PMID:22219196. CG6673 is now
  FlyBase GstO2 (Q9VSL5/Q9VSL4). Hossain et al. 2023 make this explicit
  PMID:37389657.
  Therefore the parkin / ATP synthase beta glutathionylation / DHAR in vivo findings of
  PMID:22219196 belong to GstO2, not to this gene. The only CG6662 statements in that
  paper are that its function was unknown, that it is mainly expressed in ovary and testis
  PMID:22219196,
  and a negative result
  PMID:22219196.

Enzymology

• Kim et al. 2006 (PMID:16712527, full text) cloned five Omega GST candidates from the
  sepia locus, including CG6662, expressed them in E. coli and assayed them:
  PMID:16712527
  So CG6662 has GSH-dependent thiol transferase and dehydroascorbate reductase (DHAR)
  activity, weak CDNB-conjugating activity, and no PDA (pyrimidodiazepine) synthase
  activity. (The per-enzyme values of Table 2 are not in the cached text.)
• Saisawang et al. 2012 (PMID:22082028, abstract only) expressed and kinetically surveyed the
  Drosophila cytosolic GST proteome; FlyBase curated GST activity and glutathione metabolic
  process to GstO1 from this paper
  PMID:22082028.
• Sequence: GstO1 has the Omega-class N-terminal extension and the active-site motif
  C30-P-Y-A (residues 30-33 of Q9VSL6, from the UniProt sequence), consistent with the
  catalytic cysteine of Omega GSTs PMID:16712527.
  InterPro IPR005442 (GST_omega), PANTHER PTHR43968:SF6, CDD cd03184 GST_C_Omega.

In vivo function

• Protein S-glutathionylation of the BMP ligand Gbb (Hossain et al. 2023, PMID:37389657, full text).
  An RNAi screen in postsynaptic muscle identified GstO1; null mutants (CRISPR GstO1[6-11],
  piggyBac insertion) are viable and fertile but have NMJ overgrowth with increased BMP
  signalling (pMad). GstO1 binds Gbb (co-IP with endogenous Flag-GstO1) and is needed for
  Gbb glutathionylation
  PMID:37389657.
  Glutathionylation at Gbb Cys354/Cys420 promotes Ctrip-dependent ubiquitination and
  proteasomal degradation; Grx1 opposes GstO1. Note that a cell-free assay with
  recombinant GstO1 was not reported; the in vitro glutathionylation of the Gbb fragment
  used diamide/GSH chemically.
• Localisation. In larval muscle GstO1 co-localises with the ER marker KDEL and partly
  with Rab5 and Rab11 endosomes
  PMID:37389657.
  The protein has no predicted signal peptide or TM segment in UniProt, so this is most
  likely association with the cytosolic face of these membranes.
• Oxidative stress (Lee et al. 2015, PMID:26024591, abstract only). GstO1 is highly
  expressed in adult heads; loss-of-function flies are H2O2-sensitive, rescued by
  neuronal GstO1, with reduced ERK/MAPK activation
  PMID:26024591.
• Ethanol sedation (Choi et al. 2018, PMID:30347459, abstract only). GstO1 mutants are
  hypersensitive to ethanol sedation; neuronal (dopaminergic/serotonergic) knockdown
  reproduces it PMID:30347459.
• Review (Kim et al. 2017, PMID:29435097) summarises the Drosophila GstOs and states that all
  isoforms have high thiol transferase and DHA reductase activities
  PMID:29435097.
• Hanna et al. 2015 (PMID:25585352) report "GSTO1" up-regulation in dopamine synthesis
  mutants; gene identity relative to FlyBase GstO1 vs GstO2 was not checked and the paper is
  expression-only, so it is not used for annotation.
• Cha et al. 2022 (PMID:36437507, abstract only; gene name stripped from the abstract text)
  reports GSTO knockdown increasing Cabeza/FUS mislocalisation; which GstO was studied cannot
  be determined from the cached abstract, so it is not used.

Summary

GstO1 is an Omega-class GST with the classic Omega activities (GSH-dependent thiol
transferase / DHAR, weak CDNB conjugation) and no PDA synthase activity. Its best-characterised
in vivo role is promoting S-glutathionylation of the BMP ligand Gbb in muscle, which targets
Gbb for ubiquitin-proteasome degradation and restrains NMJ growth. Loss-of-function also
causes H2O2 and ethanol hypersensitivity (abstract-level data).